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Cyronak, T, Andersson AJ, Langdon C, Albright R, Bates NR, Caldeira K, Carlton R, Corredor JE, Dunbar RB, Enochs I, Erez J, Eyre BD, Gattuso JP, Gledhill D, Kayanne H, Kline DI, Koweek DA, Lantz C, Lazar B, Manzello D, McMahon A, Melendez M, Page HN, Santos IR, Schulz KG, Shaw E, Silverman J, Suzuki A, Teneva L, Watanabe A, Yamamoto S.  2018.  Taking the metabolic pulse of the world's coral reefs. Plos One. 13   10.1371/journal.pone.0190872   AbstractWebsite

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.

Eyre, BD, Andersson AJ, Cyronak T.  2014.  Benthic coral reef calcium carbonate dissolution in an acidifying ocean. Nature Climate Change. 4:969-976.   10.1038/nclimate2380   AbstractWebsite

Changes in CaCO3 dissolution due to ocean acidification are potentially more important than changes in calcification to the future accretion and survival of coral reef ecosystems. As most CaCO3 in coral reefs is stored in old permeable sediments, increasing sediment dissolution due to ocean acidification will result in reef loss even if calcification remains unchanged. Previous studies indicate that CaCO3 dissolution could be more sensitive to ocean acidification than calcification by reef organisms. Observed changes in net ecosystem calcification owing to ocean acidification could therefore be due mainly to increased dissolution rather than decreased calcification. In addition, biologically mediated calcification could potentially adapt, at least partially, to future ocean acidification, while dissolution, which is mostly a geochemical response to changes in seawater chemistry, will not adapt. Here, we review the current knowledge of shallow-water CaCO3 dissolution and demonstrate that dissolution in the context of ocean acidification has been largely overlooked compared with calcification.

McLeod, E, Anthony KRN, Andersson A, Beeden R, Golbuu Y, Kleypas J, Kroeker K, Manzello D, Salm RV, Schuttenberg H, Smith JE.  2013.  Preparing to manage coral reefs for ocean acidification: lessons from coral bleaching. Frontiers in Ecology and the Environment. 11:20-27.   10.1890/110240   AbstractWebsite

Ocean acidification is a direct consequence of increasing atmospheric carbon dioxide concentrations and is expected to compromise the structure and function of coral reefs within this century. Research into the effects of ocean acidification on coral reefs has focused primarily on measuring and predicting changes in seawater carbon (C) chemistry and the biological and geochemical responses of reef organisms to such changes. To date, few ocean acidification studies have been designed to address conservation planning and management priorities. Here, we discuss how existing marine protected area design principles developed to address coral bleaching may be modified to address ocean acidification. We also identify five research priorities needed to incorporate ocean acidification into conservation planning and management: (1) establishing an ocean C chemistry baseline, (2) establishing ecological baselines, (3) determining species/habitat/community sensitivity to ocean acidification, (4) projecting changes in seawater carbonate chemistry, and (5) identifying potentially synergistic effects of multiple stressors.

Bates, NR, Amat A, Andersson AJ.  2010.  Feedbacks and responses of coral calcification on the Bermuda reef system to seasonal changes in biological processes and ocean acidification. Biogeosciences. 7:2509-2530.   10.5194/bg-7-2509-2010   AbstractWebsite

Despite the potential impact of ocean acidification on ecosystems such as coral reefs, surprisingly, there is very limited field data on the relationships between calcification and seawater carbonate chemistry. In this study, contemporaneous in situ datasets of seawater carbonate chemistry and calcification rates from the high-latitude coral reef of Bermuda over annual timescales provide a framework for investigating the present and future potential impact of rising carbon dioxide (CO(2)) levels and ocean acidification on coral reef ecosystems in their natural environment. A strong correlation was found between the in situ rates of calcification for the major framework building coral species Diploria labyrinthiformis and the seasonal variability of [CO(3)(2-)] and aragonite saturation state Omega(aragonite), rather than other environmental factors such as light and temperature. These field observations provide sufficient data to hypothesize that there is a seasonal 'Carbonate Chemistry Coral Reef Ecosystem Feedback' (CREF hypothesis) between the primary components of the reef ecosystem (i.e., scleractinian hard corals and macroalgae) and seawater carbonate chemistry. In early summer, strong net autotrophy from benthic components of the reef system enhance [CO(3)(2-)] and Omega(aragonite) conditions, and rates of coral calcification due to the photosynthetic uptake of CO(2). In late summer, rates of coral calcification are suppressed by release of CO(2) from reef metabolism during a period of strong net heterotrophy. It is likely that this seasonal CREF mechanism is present in other tropical reefs although attenuated compared to high-latitude reefs such as Bermuda. Due to lower annual mean surface seawater [CO(3)(2-)] and Omega(aragonite) in Bermuda compared to tropical regions, we anticipate that Bermuda corals will experience seasonal periods of zero net calcification within the next decade at [CO(3)(2-)] and Omega(aragonite) thresholds of similar to 184 mu moles kg(-1) and 2.65. However, net autotrophy of the reef during winter and spring (as part of the CREF hypothesis) may delay the onset of zero NEC or decalcification going forward by enhancing [CO(3)(2-)] and Omega(aragonite). The Bermuda coral reef is one of the first responders to the negative impacts of ocean acidification, and we estimate that calcification rates for D. labyrinthiformis have declined by > 50% compared to pre-industrial times.